Technical Field
The present invention relates to a door opening and closing apparatus for a vehicle.
Related Art
A known door opening and closing apparatus for a vehicle includes a support member interposed between a back door which opens or closes a rear opening portion of the vehicle and a body of the vehicle, and can hold the back door at an open position by the support member (see JP 2014-101637 A, for example). The support member includes an inner cylinder and an outer cylinder which are disposed concentrically and are slidably engaged with each other by fitting engagement. In the inside of the inner cylinder, elements such as an electric motor which generates a drive force, a speed reduction gear mechanism which decelerates the rotation of the electric motor are housed. In the inside of the outer cylinder, elements such as a spindle, a spindle nut, a guide tube, a coil spring, a push rod are housed. The spindle is rotatably driven by the electric motor. The spindle nut is threadedly engaged with the spindle. Due to the rotation of the spindle, the inner cylinder is moved in an axial direction together with the spindle nut and the push rod. The coil spring biases the push rod and the outer cylinder in an axial direction. The guide tube houses the coil spring therein and slidably guides the push rod.
In the door opening and closing apparatus for a vehicle which includes such a support member, in a manipulation of opening the back door in a closed state, the electric motor is driven in response to such an open manipulation. The rotation of the electric motor is transmitted to the spindle while the rotation of the electric motor is decelerated by the speed reduction gear mechanism, and the spindle is rotatably driven at a decelerated speed. When the spindle is rotated, the spindle nut is moved (pushed out) in an axial direction together with the push rod and the inner cylinder. As a result, the inner cylinder is moved relative to the outer cylinder so that the support member is extended whereby the back door is moved toward an open position. At this stage of the operation, the back door can be stopped at any desired position due to a load balance among a biasing force of the coil spring, a biasing force of a gas spring, slide resistances of the speed reduction gear mechanism and the electric motor and the like. Accordingly, the back door is held at the open position. When a manipulation of closing the back door at the open position is performed, the electric motor is rotated reversely in response to such a closing manipulation and the spindle is also rotated reversely and hence, the spindle nut is moved in a reverse direction together with the guide tube and the inner cylinder. As a result, the inner cylinder is moved (pulled) relative to the outer cylinder against a biasing force of the coil spring whereby the support member is shrunken and the door is driven to the closed position.
Conventionally, with respect to this type of support member, the electric motor which is required to possess a watertight structure for preventing leakage of electricity and the spindle, the coil spring and the like which are not required to possess high watertight property are incorporated together in the support member. When the support member adopts such a structure, it is necessary to assemble all parts through consistent manufacturing steps. Accordingly, conventionally, a manufacturing step control of this type of support member is not easy so that productivity of the support member is low.
Further, an opening/closing angle, a mounting point and the like differ for respective vehicle types and hence, when it is necessary to provide support members having different lengths for the respective vehicle types, it is necessary to change the structure of the whole support member. Such a change of the structure pushes up a cost of the support member.